The present invention relates to a process for the manufacture of fluorinated alcohols as well as novel borates which are employed in the manufacture of the fluorinated alcohols.
Polyfluoroalcohols such as RfCH2OH and RfCH2CH2OH, where Rf represents a perfluoroalkyl group, are important commercial materials. Fluorinated alcohols are used as pharmaceuticals, inhalation anesthetics, herbicides, polymers, refrigerants, etchants, lubricants, heat transfer fluids, and the like. See, for example, Banks, R. E. et al “Organofluorine Chemistry, Principles and Commercial Applications” Plenum Press, New York and London, 1994, which is incorporated herein by reference. In particular, fluorinated butanols are desirable for use in the syntheses of pharmaceutical drug candidates and for use as solvents for photographic sensitizing dyes and in epoxidation and Diels-Alder reactions. See, for example, U.S. Pat. No. 3,756,830, Fluorinated alcohols: effective solvent for uncatalyzed epoxidations with aqueous hydrogen peroxide, Synnlett, vol. 2, (2001), pp. 248-(250; and Cativiela, C., et al., Fluorinated alcohols as solvents for Diels-Alder reactions of chiral acrylates Tetrahedron:Assymetry, 4(7), (1993), pp. 1613–18, each of which is incorporated herein by reference. U.S. Pat. Nos. 6,187,969 and 6,294,704, incorporated herein by reference, describe the preparation of fluoropropanols and fluorobutanols by reacting tetrafluoroethylene or hexafluoropropylene with methanol in the presence of a free radical generator and under a relatively high pressure (from about 0.2 MPa to about 1.2 MPa). However, there is rising concern over the environmental fate of the higher homologs (Rf having 6 or more carbon atoms). Alternatives to these materials include the use of lower homologs or related materials that are not fully fluorinated. The rationale for the use of fluoroalkyl groups having one or more hydrogen atoms is that a degradation pathway is made available that leads to smaller perfluorinated fragments that have little or no tendency to accumulate in living organisms (see G. G. Moore, M. A. Yandrasits, J. F. Schulz, and R. M. Flynn, PCT WO 02/16306 A2). For example, acrylates derived from a mixture of (CF3)2CFCFHCF(CF3)CH2OH and (CF3)2CFCF(CHFCF3)CH2OH were used to provide textile treatment formulations (A. Katsushima, I. Hisamoto, S. Fukui, and M. Nagai, see U.S. Pat. No. 3,457,247; 1969). The above-mentioned alcohols were reportedly prepared by the benzoyl peroxide catalyzed addition of methanol to (CF3)2CFCF═CFCF3 (see N. Ishikawa, A. Nagashima, S. Hayashi, Nippon Kagaku Kaishi (1974), 7, 1240; CA (1974) 81:119432 and U.S. Pat. No. 3,457,247; 1969). However, Kurykin et al. noted that this procedure failed under the conditions reported (see M. A. Kurykin, L. S. German, L. I. Kartasheva, and A. K. Pikaev, J. Fluorine Chemistry, 77 (1996) 193). They used gamma-irradiation to catalyze the addition of methanol to the olefin either without a solvent or with methyl trifluoroacetate as the solvent. Both processes have problems for large-scale use, the latter (method of Kurykin et al.) due to the method of radical generation, and the former because the process lacks robustness. Part of the difficulty may be due to reaction non-homogeneity in the absence of a solvent, but the latter is undesirable for a variety of reasons. Chambers et al. successfully added dimethyl carbonate to hexafluoropropene using a peroxide initiator, while trimethyl borate was added to hexafluoropropene using gamma irradiation (see R. D. Chambers, B. Grievson, and N. M. Kelly, J. Chem. Soc. Perkin Trans. 1 (1985) 2209). Dimethyl carbonate and trimethyl borate may be thought of as methanol equivalents since, when the adducts are hydrolyzed, the hydrolysis products are the same as one would obtain from the addition of the hydroxymethyl radical (from methanol itself) to hexafluoropropene. It should be noted however, that in the case of hexafluoropropene, the radical addition of methanol is reliable. In contrast, it has been discovered that when (CF3)2CFCF═CFCF3 (HFP dimer) was used instead of hexafluoropropene, poor results (poor conversion, yield, or complicated workup) were obtained, not only for methanol itself but also for methanol equivalent reagents including dimethyl carbonate and methyl t-butyl ether. Initiators included benzoyl peroxide, AIBN, t-butyl perbenzoate, and t-butyl peroxide. Surprisingly, trimethyl borate did provide a practical yield of the desired alcohol following hydrolysis of the borate adducts.